1. Field of the Invention
The present invention primarily relates to a dielectric ceramic composition used in a high frequency range including, for example, pseudo-microwaves, microwaves, millimeter waves, and sub-millimeter waves. Preferably, the present invention is applied to, for example, a high frequency dielectric ceramic composition constituting resonators, oscillators, filters, and circuit boards in satellite communication equipment, mobile communication equipment, wireless communication equipment, RF communication equipment, and their base stations.
2. Description of the Background Art
It is well known that high-frequency dielectric ceramic compositions are generally used in high-frequency devices, such as resonators, oscillators, and filters for current high-frequency communications operated fairly in the pseudo-microwave or microwave regime. In general, the high-frequency dielectric ceramic composition is desired to have a high dielectric constant (xcex5r), a near-zero temperature coefficient of resonant frequency (xcfx84f), and a high Q-factor.
BaOxe2x80x94TiO2xe2x80x94SnO2-based materials described in U.S. Pat. No. 4,548,910 (1985) and BaOxe2x80x94TiO2xe2x80x94Nd2O3xe2x80x94Bi2O3xe2x80x94Nb2O3xe2x80x94MnO-based materials described in Japanese Patent No. 2977707 (1999) have conventionally been used as a typical high-frequency dielectric ceramic composition. A dielectric ceramic composition with the complex perovskite structure is known as a material having a higher Q-factor in the high frequency range.
Recently, demands for high-speed communication or an increase in the number of communication channels causes requirements of higher operation frequency for communication. Because of these increase in frequency bands, development of a dielectric ceramic composition having a higher Q-factor has been become more important. However, conventional high-frequency dielectric ceramic compositions have not possessed practical Q-factors in the millimeter band or the sub-millimeter band. High power consumption caused by a low Q-factor of a conventional high-frequency dielectric ceramic composition leads to the short operating time of a battery. Thus, power savings in electronic components or portable terminals have been hindered. Most of dielectric ceramic compositions have such a characteristic that the product of frequency (f) and Q-factor (Q), that is, Qf is a constant value. An increase of an operation frequency, therefore, causes a decrease of Q-factor.
Even if a new development of a dielectric ceramic composition having a high Q-factor is attempt in order to solve the above-described problem, there are no means to investigate which dielectric ceramic composition has the potential to attain a high Q-factor. Since there exist no guidelines or principles for developing a new dielectric ceramic composition, there has been no alternative but to experimentally try combinations of various elements. In this process, enormous amounts of development time and costs have been wasted.
The following dielectric ceramic compositions have already been developed; namely, Ba (Co1/3Nb2/3)O3-based materials (Qf of 60000GHz) described in Japanese Journal of Applied Physics Vol. 24, 1985; Ba(Co1/3Ta2/3)O3-based materials (Qf of 46200 GHz) and Ba(Ni1/3Ta2/3)O3-based materials (Qf of 49700 GHz) described in Journal of American Ceramic Society Vol. 66, 1983; Ba(Mg1/3Nb2/3)O3-based materials (Qf of 55400 GHz), Ba(Mn1/3Nb2/3)O3-based materials (Qf of 900 GHz), and Ba(Zn1/3Nb2/3)O3-based materials (Qf of 86900 GHz) described in Ferroelectrics Vol. 49, 1983; Ba(Mg1/3Ta2/3)O3-based materials (Qf of 200000 GHz) described in Examined Japanese Patent Publication No. 7-84347/(1995); Ba(Mn1/3Ta2/3)O3-based materials (Qf of 109200 GHz) described in Japanese Journal of Applied Physics Vol. 23, 1984; Ba(Ni1/3Nb2/3)O3-based materials (Qf of 480000 GHz) described in Journal of Material Research Vol. 12, 1997; and Ba(Zn1/3Ta2/3)O3-based materials (Qf of 169200 GHz) described in Examined Japanese Patent Publication No. 7-5778/(1993). For the purpose of comparison, example dielectric characteristics of the known high-frequency dielectric ceramic compositions are summarized in Table 1.
These materials have embodied a composition having a maximum Qf of about 200000 GHz. Improvements have been made only in terms of impurities to be mixed or contained with the materials and manufacturing methods. No attempt has been succeeded to manifest the atomic coordinate structure of a high-frequency dielectric ceramic composition crystal or the correlation between atomic coordinate structure and Qf.
The present invention is aimed at solving the foregoing problems and providing a dielectric ceramic composition suitable for achieving a high Q-factor in a high-frequency range. Further, the present invention is aimed at providing a method of designing a dielectric ceramic composition which enables short-term, and inexpensive development of a new dielectric ceramic composition which will possess a high Q-factor in a high frequency range.
To this end, the present invention provides a dielectric ceramic composition formed primarily from a complex perovskite dielectric ceramic composition A2+(Bxe2x80x22+1/3Bxe2x80x35+2/3)O2xe2x88x923 and having a hexagonal triple superlattice structure, wherein a difference between the lattice energy EORD per unit atom of the hexagonal triple superlattice structure which is formed in a case where Bxe2x80x22+ ions and Bxe2x80x35+ ions are ordered in the 1:2 B-site sequence and the lattice energy EDIS per unit atom of a simple perovskite structure formed when the B-site of the complex perovskite dielectric ceramic composition has a disordered configuration or that of a model structure approximated to a disordered configuration; that is, xcex94EDISxe2x88x92ORD, satisfies the following equation
xcex94EDISxe2x88x92ORD=EDISxe2x88x92EORDxe2x89xa777.8(meV/atom)xe2x80x83xe2x80x83(1).
Further, the present invention provides a method of designing a dielectric ceramic composition comprising the steps of: optimizing the crystal structure of the dielectric ceramic composition such that the lattice energy of a crystal structure having an ordered configuration is minimized; optimizing the crystal structure of the dielectric ceramic composition such that the lattice energy of a disordered crystal structure or the lattice energy of a model structure approximated to the disordered configuration is minimized; and determining an absolute value of a difference between lattice energy EORD per unit atom of the thus-optimized ordered crystal structure and lattice energy EDIS per unit atom of the thus-optimized disordered structure or the thus-optimized model structure approximated to the disordered configuration; that is, |xcex94EDISxe2x88x92ORD|, to thereby estimate Q-factor of a dielectric ceramic composition and design a dielectric ceramic composition having a high Q-factor.
Preferably, the dielectric ceramic composition Ap+x(Bxe2x80x2q+yBxe2x80x3r+1xe2x88x92y)zO2xe2x88x92w satisfies w=0.5xc3x97(pxc3x97x+(qxc3x97y+rxc3x97(1xe2x88x92y))xc3x97z) and 0xe2x89xa6yxe2x89xa61. Further, the ordered structure of the dielectric ceramic composition is formed from y:(1xe2x88x92y) arrangement over the B-site of the dielectirc composition.
Preferably, there is designed a complex perovskite composition A2+(Bxe2x80x22+1/3Bxe2x80x35+2/3)O2xe2x88x923.